Plugin Screenshots Downloading?

It’s not you, it’s SVN. And you.

The tl;dr is that the MIME Types on your images aren’t correct. Per Otto:

On Windows, using TortoiseSVN, you can right click the screenshot file, and select the TortoiseSVN->Properties menu. There you will find the svn:mime-type property, probably incorrectly set to “application/octet-stream”. Change that to the proper mime type of “image/png” or “image/jpg” accordingly. Afterwards, commit the change.

If you prefer command line SVN:

svn propset svn:mime-type image/png screenshot-1.png
svn commit

Or similar. If somebody uses a different SVN client, look for “properties” and then the svn:mime-type property.

Once you do that, upload the changes and go make coffee. The information will sync out, but it may take a little while.